Heretofore, aluminium or an aluminium alloy has been generally used as the wiring material for display devices such as flat panel displays, etc. However, with growing in size and increasing in resolution of displays, there has occurred a problem of RC delay caused by the characteristics such as the wiring resistance of such aluminium-based wiring materials and uniform panel displaying has tended to be difficult.
Given the situation, the recent tendency is toward investigation of employing copper or copper-based wiring with a material having a lower resistance. However, copper has an advantage in that its resistance is low but, on the other hand, has a problem in that, in use for gate wiring, the adhesiveness between the substrate such as glass or the like and copper is not sufficient and that, in use for source/drain wiring, copper may diffuse into the silicon semiconductor underlayer. Consequently, for preventing these, there has been made an investigation of barrier layer lamination with a metal that has high adhesion to a substrate such as glass or the like, and hardly diffuses into the silicon semiconductor underlayer and additionally has a barrier property; and as the metal, titanium-based metals such as titanium (Ti) and titanium nitride (TiN) have become specifically noted.
A multilayer film that contains copper or a copper-based copper alloy is formed on a substrate of glass or the like according to a film formation process of a sputtering method or the like, and then processed in an etching process of etching it via a resist serving as a mask to give an electrode pattern. The etching process includes a wet etching mode of using an etching liquid and a dry etching mode of using an etching gas of plasma or the like. The etching liquid for use in the wet mode is desired to satisfy the following: (i) The processing accuracy is high, (ii) the amount of the etching residue is small, (iii) the etching unevenness level is low, and (iv) the etching ability to dissolve the metal of the copper-containing wiring material to be etched is stable; and in addition to these, for meeting the size enlargement and the resolution enhancement of displays, (v) the wiring configuration formed after etching could fall within a predetermined range, or that is, a good wiring configuration can be obtained. More concretely, the parameters shown in FIG. 1 are desired to be as follows: The angle (taper angle) between the etched face of the copper wiring edge and the underlayer substrate is from 20 to 60°, or that is, the angle is a regular taper angle; the distance between the resist edge and the wire edge to be in contact with the resist (top CD loss, a×2) is at most 3 μm, the distance between the resist edge and the wire edge to be in contact with the barrier layer provided below the wire (bottom CD loss, b×2) is at most 1 μm, and the barrier film tailing (c) is not more than b.
As the etching liquid to be used in the etching process for the multilayer film containing copper or a copper-based copper alloy, for example, there have been proposed an etching solution containing at least one selected from a neutral salt, an inorganic acid and an organic acid, and hydrogen peroxide and a hydrogen peroxide stabilizer (for example, Patent Reference 1), an etching solution containing hydrogen peroxide, an organic acid and fluorine (for example, Patent Reference 2), etc.
However, these are all unsatisfactory in point of the wiring profile after etching therewith and, as a result, could not often sufficiently meet the size enlargement and the resolution enhancement of displays.